Numerous different trenching apparatus are known. Some representative examples include those described in U.S. Pat. No. 3,099,098, DE 4 243696, WO99/54556, WO20013/088167, GB 2 495 950, EP 1167636 and NL 9201058.
EP 1167636 describes a trenching apparatus with a centrally mounted trench cutting device. The apparatus is mounted on wheels or skids via respective four-bar suspension assemblies which can be extended laterally from a main body of the apparatus.
NL9201058 describes a trenching apparatus for underwater trenches. The apparatus has a main body to which a trench cutting tool is mounted. The main body is mounted on four endless track units. Each endless track unit can adjusted relative to the main body portion for height, direction and lateral spacing.
Problems can occur with trenching apparatus in dealing with uneven topography of the ground or land in which the trench is to be cut. Herein “land” or “ground” can refer to the seabed when the trenching apparatus is configured for underwater use. Such uneven topography can include slopes which the trenching apparatus must traverse and local features of the land (e.g. seabed) which can project upwardly in the path of the trenching apparatus, such as ridges, boulders and the like.
Such uneven topography can cause difficulties in relation to the trench cutting equipment of the trenching apparatus. In some typical configurations, the trench cutting equipment is mounted to the trenching apparatus in such a way that it can be raised and lowered in a vertical plane, normally so that the trench cutting equipment can be moved between stowed and use positions, for example. However, the trench cutting equipment can typically otherwise be mounted in fixed angular relation to a main body part of the trenching apparatus. It follows that if the angular position of the main body portion changes, the angular orientation of the trench cutting equipment is also changed. Such change in angular orientation of the trench cutting equipment can have significant consequences in relation to the trench being cut. In particular, changes in the angle of orientation of the trench cutting equipment can cause the walls of the trench as cut to be formed at an angle other than a desired cutting angle. Commonly, the desired cutting angle is vertical. Such departure from the desired cutting angle (in particular departure form a vertical cutting angle) can lead to a reduction in, or loss of, stability of the walls, so that the trench can collapse.
In other known devices, such as that described in WO99/54556, the trench cutting equipment can be mounted to allow movement about a nominally longitudinal horizontal axis relative to the main body portion of the trenching apparatus. In analogous manner, U.S. Pat. No. 3,099,098 describes a trenching apparatus having trench cutting equipment in angularly fixed relation to a main body of the apparatus. The main body is mounted to a chassis, the main body being moveable with respect to the chassis about a longitudinal horizontal axis. In these prior art constructions, some compensation for angular displacement of the main body portion can be achieved and the trench cutting equipment can generally be maintained in a nominally vertical orientation. However, such arrangements do not compensate for lateral displacement of the trench cutting equipment which can occur when the main body portion of the trenching apparatus changes its angular orientation.
Some embodiments of the present invention seek to address one or more of the above problems. Embodiments of the present invention can provide a trenching apparatus which can accommodate variations in the topography of the ground, notably the seabed, to better maintain a desired angular orientation of the trench cutting equipment (in particular, a vertical orientation).
Embodiments of the present invention can provide a trenching apparatus which can accommodate variations in the topography of the ground, notably the seabed, to avoid, reduce or minimise unintended or undesired lateral displacement of the trench cutting equipment from an intended trenching course or path.
Embodiments of the invention can provide a trenching apparatus which can accommodate variations in the topography of the ground, notably the seabed, such that angular displacement of a main body portion of the trenching apparatus, to which trench cutting equipment is mounted, is minimised, reduced or prevented.
Particular embodiments of the invention can provide a trenching apparatus which can in effect pivot substantially about its virtual centre point in order to maintain a desired angular orientation to the trench cutting equipment.
Embodiments of the apparatus of the invention can include a suspension assembly arranged between a main body of the apparatus and a ground contacting unit on which the apparatus stands. Respective suspension assemblies can be configured such that the trenching apparatus (or at least the main body portion thereof) can in effect pivot substantially about its virtual centre point in order substantially to maintain a desired angular orientation to the trench cutting equipment irrespective of variations in the topography of the underlying ground. The desired angular orientation of the trench cutting equipment can be a nominally vertical orientation. The desired orientation of the trench cutting equipment can be maintained by maintaining a desired orientation of a main body portion of the trenching apparatus, to which the trench cutting equipment is mounted.
Embodiments of the present invention can provide a trenching apparatus including a virtual pivot system, and such system can have a pivot centre substantially on the centre line of the trench cutting equipment. In some preferred constructions, the centre line of the trench cutting equipment can be coincident with the centre line of the trenching apparatus.
In particular embodiments of the invention, the virtual pivot, as can be embodied by the respective suspension assemblies, can preferably be optimised to:
keep the main body portion angular displacement minimal with respect to the direction due to the acceleration due to gravity and/or
minimise the distance variation between the tool ground engagement point and the ground contacting units (that is, to minimise lateral displacement) and/or
to allow the ground contacting unit rotate to keep the ground contacting unit in a condition in which the ground contacting face thereof is maintained substantially parallel to the ground on which the ground contacting unit stands.